Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant
certifies that it meets all the requirements for effectiveness of this post-effective amendment pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this registration statement to be signed on its behalf by the undersigned,
thereunto duly authorized, in the City of Chicago and State of Illinois on May 22, 2013.

COLUMBIA ACORN TRUST

By

/S/ CHARLES P.
MCQUAID

Charles P. McQuaid, President

Pursuant to the requirements of the Securities Act of 1933, this amendment to the registration
statement has been signed below by the following persons in the capacities and on the dates indicated.